Shrinking integrated circuits (ICs) may result in improved performance, increased capacity and/or reduced cost. Each device shrink requires more sophisticated techniques to form the features. Photolithography is commonly used to pattern features on a substrate. An exemplary feature is a line of a material which may be a metal, semiconductor or insulator. Linewidth is the width of the line and the spacing is the distance between adjacent lines. Pitch is defined as the distance between a same point on two neighboring lines. The pitch is equal to the sum of the linewidth and the spacing. Due to factors such as optics and light or radiation wavelength, however, photolithography techniques have a minimum pitch below which a particular photolithographic technique may not reliably form features. Thus, the minimum pitch of a photolithographic technique can limit feature size reduction.
Self-aligned double patterning (SADP) is one method for extending the capabilities of photolithographic techniques beyond their supposed minimum pitch. Such a method is illustrated in FIGS. 1A-1H. With reference to FIG. 1A, patterned features 102 are formed from sacrificial structural material above a dielectric layer (or more generally an underlying layer or underlayer 114) on a substrate 101 using standard photo-lithography and etching techniques. The patterned features are referred to as placeholders, mandrels or cores and have linewidths and/or spacings near the optical resolution of a photolithography system using a high-resolution photomask. As shown in FIG. 1B, a conformal layer 106 of hard mask material is subsequently deposited over cores 102. Hard mask spacers 108 are then formed on the sides of cores 102 by preferentially etching the hard mask material from the horizontal surfaces with an anisotropic spacer etch. The resulting structure is shown in FIG. 1C. Cores 102 may then be removed, leaving behind hard mask spacers 108 (FIG. 1D). At this point hard mask spacers 108 may be used as an etch mask for transferring the pattern to underlayer 114 to form dielectric ribs 116, as shown in FIG. 1E. The hard mask spacers 108 are subsequently removed (FIG. 1F).
The density of the dielectric ribs 116 is twice that of the photo-lithographically patterned features 102, the pitch of dielectric ribs 116 is half the pitch of patterned features 102. A metal layer 130 is deposited over the dielectric ribs 116 and exposed portions of the substrate 101 (FIG. 1G) and subsequently etched back or polished to form metal lines 132 between the dielectric ribs 116 as shown in FIG. 1H. Methods are needed to improve the uniformity and yield of density increasing techniques such as the technique of FIGS. 1A-1H.